The present invention is directed to substantial reduction of unreacted ammonia and the corresponding reduction in ammonium sulfate and resulting waste products produced from the unreacted ammonia during the manufacture of acrylonitrile by the direct ammoxidation of an unsaturated or saturated hydrocarbon, preferably propylene or propane, ammonia and oxygen in a fluid bed reactor containing an ammoxidation catalyst. In particular, the present invention is directed to the addition of an oxygen containing gas, preferably air, at a specific location in the fluidized bed reactor during the manufacture of acrylonitrile to reduce substantially the amount of ammonia remaining in the gaseous effluents exiting the fluidized bed reactor during the manufacture of acrylonitrile. This process is carried out in the absence of any additional oxygenated hydrocarbon compound such as methanol. This substantial reduction in the generation of ammonium sulfate during the practice of the manufacture of acrylonitrile leads to significant environmental and economic advantages.
There are several patents which are directed to the injection of methanol into a fluid bed reactor to produce hydrogen cyanide. In addition, these references further disclose the injection of methanol into an acrylonitrile fluid bed reactor to produce hydrogen cyanide while manufacturing acrylonitrile. For example, U.S. Pat. Nos. 3,911,089 and 4,485,079 each teach the ammoxidation of methanol to produce hydrogen cyanide by injection of methanol into a fluid bed reactor containing an ammoxidation catalyst suitable for the manufacture of acrylonitrile. Moreover, Japanese Patent Applications 74-87474, 79-08655 and 78-35232 all are related to similar methods of increasing or making hydrogen cyanide during the manufacture of acrylonitrile. Japanese Patent Application 74-87874 also suggests that a secondary effect of their procedure is the decrease of the amount of sulfuric acid used for neutralization. All of these patents are primarily concerned with the production of additional hydrogen cyanide. Finally, U.S. Pat. No. 5,288,473 and copending applications U.S. Ser. No. 08/187,425 filed Jan. 26, 1994 and U.S. Ser. No. 08/104,752 filed Aug. 11, 1993, all assigned to the assignee of the present invention, are directed to the substantial reduction of the amount of unreacted ammonia exiting the fluid bed reactor which utilized oxygenate compounds such as methanol while Chinese Patent CN 1032747 to Sun et al. discloses multi-staged air feed to a reactor to increase acrylonitrile conversion.
The present invention is directed to a specific procedure for injection of an oxygen containing gas, preferably air, into the fluid bed reactor to obtain a substantial reduction in the amount of unreacted ammonia exiting the fluid bed reactor during the manufacture of acrylonitrile without any decrease in the acrylonitrile yield. The process is performed in the absence of any oxygenated hydrocarbon compounds such as methanol.